1. Field of the Invention
The present invention relates to a recording medium output apparatus for outputting a sheet-like recording medium being transported onto a stack tray on which recording media are stacked and to an image forming apparatus provided with the recording medium output apparatus.
2. Description of the Related Art
A recording medium output apparatus is assembled to an image forming apparatus such as a copy machine, a facsimile, a printer, and the like using an electrophotographic system to output a sheet-like recording medium (for example, a sheet and the like). There is a recording medium output apparatus provided with an output unit movable in a sheet width direction so that, when plural sets of copies are made from plural documents, the sets of copies can be easily sorted by being output after the copies of each set are offset in a sheet width direction perpendicular to the transport direction thereof. In the recording medium output apparatus having the output unit movable in the sheet width direction, the output unit begins to move after the lead edge of a sheet leaves the output unit. The sheet is continuously output while the output unit is being moved, and the trail edge of the sheet leaves the output unit after the output unit stops at a predetermined offset position.
However, since the output unit, which moved until that time, stops, a force, which acts in a direction opposite to the moving direction of the output unit, acts on the trail edge of the sheet just before the trail edge of the sheet leaves the output unit, whereas an inertia force, which is generated by the movement of the output unit and acts in the moving direction of the output unit, acts on the lead edge of the sheet. Accordingly, a turning force acts on the sheet just after the trail edge thereof leaves the output unit so as to direct the lead edge of the sheet in the moving direction and the trail edge thereof in the direction opposite to the moving direction. Although the sheet output from the output unit falls onto a stack tray on which sheets are stacked, the attitude of the sheet fallen onto the tray may be disturbed by the turning force. When sheets are disturbed on the stack tray, the boundaries among respective sets of sheets become obscure or an amount of offset is reduced due to the disturbance of the attitude of the sheets, which makes sorting difficult.
By the way, the amount of offset in the sheet width direction is determined by the size (machine size) of an image forming apparatus to which the recording medium output apparatus is assembled. Accordingly, when it is intended to increase the amount of offset to execute sorting more easily even if slightly, the machine size must be increased, which prevents the reduction of the size and the cost of the image forming apparatus. To cope with the above problem, there are proposals for suppressing the dispersed attitudes of sheets to execute sorting more easily even if slightly without increasing the amount of offset (refer to for example, Japanese Patent Application Laid-Open Publications Nos. 8-208098, 8-208091, 1-214565, and 62-249858). These proposals intend to improve the alignment of sheets by guiding the trail edges of the sheets output from an output unit, by guiding the trail edges of the sheets before and after they are output from the output unit, or by devising the shape of the output unit. Therefore, it is contemplated to combine the recording medium output apparatus, in which the turning force acts on a sheet just after it is output, with these proposals.
However, it is desired to increase the amount of offset to execute sorting more easily.
The present invention has been made in view of the above circumstances and provides a recording medium output apparatus, in which an amount of offset is increased without increasing a machine size as well as a sheet alignment capability is enhanced, and an image forming apparatus provided with the recording medium output apparatus.